Heating device



May 23, 1944. J. R. CAMPBELL HEATING DEVICE Filed Feb. 25. 1943 1 x 1 I I l 1 1 1 l 1 r 1 I 1 1 a I w p vm n a r M e MM vsw/ ne w aw J B Patented May 23, 1944 HEATING nnvrca James R. Campbell, Ontario, CaliL, asslgnor to General Electric Company,

New York a corporation of Application February 2a, 194:, Serial No; 476,825

6 Claims. (01. 219-46) pad with a thermally responsive element ar-" ranged to control the energization of the heating pad circuit responsively to the pad temperature. In order to control the pad temperature, I provide auxiliary heating means for supplying heat to the temperature responsive element in addition to that which it receives from the pad. By controlling the amount of heat supplied to the element from the auxiliary source, the pad temperature is controlled.

For thus controlling the auxiliary heat, the temperature responsive element is provided with a plurality of sections having diflerent heating agencies. These agencies operate selectively, and each functions to deflect the thermally-responsive element at its own particular rate so as to control the proportion of time that power is supplied to the pad to the time that it is not supplied, and thereby control the pad temperature. Switch means are provided for selectively rendering these sections operative to control the operation of the temperature responsive element so that the temperature at which the pad operates can be selected at will.

, For a more complete understanding of this invention, reference should be had to the accompanying drawing in which Fig, 1 illustrates an electric heating pad provided with a temperature control device embodying this invention; and Fig.2 is an enlarged viev oi the temperature controlling element of the pad.

Referring to the drawing, this invention has been shown in one form as applied to an electric heating pad ll which is provided with a resistance conductor H forming a heating circuit for the pad. The resistance conductor II is formed into a series of convolutions, as shown, so as to distribute the generated heat over the pad area.

The pad is supplied with electrical power from' dotted lines. The temperature-responsive element I4 is of the bimetallic type, being formed by two strips of metal having dissimilar tem perature coeiilcientsof expansion and secured together lengthwise in any suitable way as by welding. The upper section of the element, as viewed in Fig. 2, is formed of the metal havin the higher temperature coeflicient of expansion so that when the element is heated-it will deflect downwardly, and when permitted to cool it will deflect upwardly. l

The temperature-responsive element It has a U-shapebeing formed with a pair of legs l6 and I1 and a nexus l8 connecting the legs at one end. The opposite ends of the legs are rigidly secured to an electrically insulating supporting member I! mounted in the casing l5. It may be secured in any suitable way, but preferably will be attached by means of-screw fastening means 2| and 2|. The nexus 18 carries a movable contact 22 which coacts with a fixed contact 23 that is adjustable with reference to the thermal blade. The contacts 22 and 23 are arranged to control the 'energization of the heating circ'uit ll of the pad responsively to the deflection of the thermostatic elernent ll.

'The thermostatic element It responds both to the temperature of the pad itself and also to its own heating agency, and it is preferably heated by the passage of electrical current through it; in other words, it is an electro-thermally responsive element. And the two legs I! and I1 constitute two operating sections for the thermostat which will move it to open and close the switch at different rates to thereby vary the power input to the pad l0 and consequently the temperature held in it. As shown, the leg Ii has a relatively small cross-section as compared with the leg i1 and, therefore, its electrical resistance is higher than that of the leg ll.

It is contemplated in the operation of the device that one, or the other, or both of the legs connected in parallel will be connected in series with the heating circuit ll so as to control its energization. For. this purpose, a manually controllable switch 24 is interposed in the connections leading from the source i2 to the pad;:it

is provided with a pair of fixed contacts 2! and 26 and a movable contact 21. The movable contact 21 may engage either the contact 2!, or the contact 26, or it may bridge them. The fixed contact 21 is connected to one side of the supply and H, as shown. The other side of the supply source is connected to one side of the heating circuit il', whereas the other side or this circuit is connected to the fixed contact 33.

In operation, when the switch contact 2'! is in its open position, as shown in Fig. 1, the pad Iii will be deenergized. If the switch contact 2! is moved to close the contact 25, the high resistance leg is will be connected in series with the heating pad circuit, because at this time the thern element li will be cold and the switch contacts 22 andilt will be closed. Inasmuch as this is the high resistance path; the thermal element M will be quickly heated to a predeter mined high temperature both by the heat imparted to it from the pad and that generated internally in the leg it. When the thermal element reaches this temperature it will open the contacts 22 and 23 which operation will de-energize the thermal element, and at the same time heating circuit, a control device therefor comprising a thermally-responsive element responsive to the temperature ofsald device and having a plurality of thermally-responsive sections that are connected to deflect in unison responsively to temperature changes and including means for heating said thermally-responsive element at different rates to cause movement thereof, means for selectively rendering said sections effective to control said thermally-responsive element, and means controlled by movements of said ther+ madly-responsive element for controlling the energization of said heating circuit.

willshut ofi the power from the pad It. Then the pad will cool, and so will the section it; and when the thermal element reaches a predetermined low temperature it will reclose the contacts Hand 23 to reenergize itself andalso the pad circuit Ii.

pad it and to shut it oii from the pad. The proportion of time that power is supplied to the time that it is shut ofi determines the temper 'ature that will be held in the pad. And inasmuch as the section it has a high resistance the proportion of time that power is supplied to the time that it is not supplied is relatively small and the pad operates at its lowest temperature setting. 7 If it be desired to operate the pad at a higher temperature, the switch contact 21 is moved to close'the contact 26 alone. This connects the low resistance section II in series with the pad .circuit, and the control device operates in the manner previously described, except that the thermal element it is heated relatively slowly by the pad and by the low resistance section 81. And the proportion of time that power is supplied to the pad it to the time that it is not supplied isgreater. Consequently,'the pad operates at a higher temperature.

A still higher pad-operating temperature may be obtained by moving the contact 21 to bridge the contacts and 26. This connects the two resistance sections it and H in parallel with each other and the two together in series circuit relation with the heating circuit N. This produces a minimum heating effect for the thermal In this way, the control de- 1 vice operates alternately to supply power to the element so that it is very slowly heated to open the circuit. Consequently; the proportion of time that the power is supplied to the time that it is not supplied is the greatest and the pad will operate at its maximum temperature.

It will be observed that I have provided a very simple and reliable construction for controlling the heating pad It to give it three operating temperatures.

While I have 'shown and described a particular embodiment of my invention, it will be understood, of course, that I'do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate bythe appended claims to cover any suchmodlfications as fall withinthe true spirit and scope of my invention. 4

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electrically heated device having a 2. In an electrically heated device having a heating circuit, a control device for said heating 3. In an electric heating pad having a heating circuit,-a control device for said heating pad comprising a temperature responsive bar responsive to the temperature of said pad and having a plurality of mechanically interconnected legs which move in unison in one direction when the bar is heated and in another direction when the bar is cooled, said legs having diiferent electrical resistances, means for selectively connecting said legs in said heating circuit so that said bar is heated to move in said one direction at different rates, and means controlled by said bar in moving in said one direction to reduce the power supplied in said circuit and thereby its heating efiect, and in moving in said other direction to increase the power supplied in said circuit and thereby its heating effect.

. 4. In an electric heating pad having a heating circuit, a control device for said circuit comprising an electro-responslve thermostatic switch connected in said circuit arranged when closed to supply power to said circuit and when opened to shut ofi the power to said circuit, and said switch having a plurality of thermally-responsive sections that respond to the temperature of said pad and which deflect to open said switch when heated and to reclose said switch when subsequently cooled, said sections having diiferent electrical resistances, and switching means for selectively connecting said sections in said circuit, one at a time, or all simultaneously, so that said thermostatic switch is operated at different rates to hold difi'erent temperatures in said pad.

5. In a heating pad having a heating circuit, a control device for said circuit comprising a u.-

shaped bimetallic bar responsive to the temperature of said pad, the two legs of said bar having ,diflerent electrical resistances, a switch in said 65.

6. In a heating pad having a heating circuit, a control device for said circuit comprising a bimetallic bar responsive to the temperatureof said pad and controlling said circuit to cut down the heat when the bar is heated to a predetermined high temperature and to increase the heat when the bar cools down to a predeterbeing free to deflect *responsivel'y to teinperature changes and said latter ends being connected to 'move together, saidlegs having difierent electrical resistances; and switching means for connecting one or the other of said legs in series with said circuit or the two legs in parallel in series with said circuit so that said bar periodically operates said switch to open at difierent rates thereby to hold diflerent temperature conditions;

JAMES R. CAMPBELL. 

